232 



MASS MUTATIONS AND TWIN HYBRIDS OF 



(table X I) and counted them in the same way as previously described, 

 in the beginning of the flowering period. The percentage figures 

 for the appearance of types R and T coi respond to those derived 

 from our table for ovata, which were 24 and 4.5. The figure for 

 lorea is a low one, but in the cross 0. grandiflora x biennis we have 

 seen that 43 per cent lorea were split off in the second generation. 



Table XI 

 Second generation of crosses of 0. grandiflora lorea; cultures of 1916 



The question whether this phenomenon conforms to the formula 

 of Mendel for monohybrids remains to be answered by more ex- 

 tensive cultures. 



F. Mass mutations, considered as secondary mutations 



After describing the facts observed in my cultures and experi- 

 ments, we may now proceed to the discussion of the principle of 

 Bartlett, already quoted. He assumed that a fundamental mutation 

 occurred in one of the two gametes in a generation preceding that 

 in which the mass mutation appeared. We are not concerned, however, 

 with the question whether all instances of mass mutation are due 

 to the same internal processes, but only with the problem of ex- 

 plaining the production of mut. ochracea from 0. grandiflora by 

 means of Bartlett's suggestion. 



In order to proceed in an empirical way, and to rely as much 

 as possible on analogy with well ascertained facts, I shall start from 

 a consideration of the mutation of Lamarckiana gigas into its 



